Because of market constraints, it is becoming more necessary to process highly acidic crudes such as acidic naphthenic crudes. It is well known that processing such acidic crudes can lead to various problems associated with naphthenic and other acid corrosion. A number of methods to reduce the Total Acid Number (TAN), which is the number of milligrams of potassium hydroxide required to neutralize the acid content of one gram of crude oil, have been proposed.
One approach is to chemically neutralize acidic components with various bases. This method suffers from processing problems such as emulsion formation, increase in sodium concentration in the crude and additional processing steps. Another approach is to use corrosion-resistant metals in processing units. This, however, involves significant expense and may not be economically feasible for existing units. A further approach is to add corrosion inhibitors to the crudes. This suffers from the effects of the corrosion inhibitors on downstream units, for example, insufficient coverage of the entire metal surface, lowering of catalyst life/efficiency and potential produce quality impact. Another option is to lower crude acid content by blending the acidic crude with crudes having a low acid content. The limited supplies of such low acid crudes makes this approach increasingly difficult.
British patent 1,236,230 discloses a process for removing naphthenic acids from petroleum distillate fractions without the addition of gaseous hydrogen by contacting the distillate fraction with a catalyst containing nickel, tungsten molybdenum, cobalt, iron or combinations thereof at mild processing conditions. U.S. Pat. No. 2,921,023 describes a process for maintaining the activity of certain molybdenum catalysts during the hydrogenation of organic materials. The catalysts may be used to hydrogenate heavy petroleum fractions in which the amounts of oxy-compounds such as naphthenic acids is reduced.
It would be desirable to reduce the acidity of crude oils without the addition of neutralization/corrosion protection agents and without converting the crude into product streams.